The mutant superheroes are back, keeping the multiplexes safe for moviegoers.

Bryan Singer's "X2," like his 2000 predecessor "X-Men," is crackling good fun, helped immensely by a topnotch cast that seem equipped with superpowers of their own — whether it be splendid acting chops, breathtaking good looks, or (hello, Wolverine) both. Though the film's energy lags a bit in its final half-hour, "X2" is a wonderfully populated adventure, with the franchise even more compelling the second time out because of our familiarity with the characters.

And as if the original batch of X-people weren't enough, "X2" introduces a few nifty new ones. Nightcrawler (Alan Cumming), with inky-blue skin covered in curlicue carvings, makes a stunning entrance, whooshing around a room like a crazed bat. He's a teleporter, vaporizing into swirls of black smoke as he instantly reappears somewhere else; throughout the movie, he emerges as a strange, haunted creature, speaking in a phlegmy German accent. Is he villain or friend in the X-universe, where labels are dangerous things? Watch and see.

More easily categorized is the hate-filled Stryker, played to the hilt by Brian Cox, so memorably villainous as Hannibal Lecter in "Manhunter." (Cox shares a Royal Shakespeare Company background with co-stars Patrick Stewart and Ian McKellen. Watching these guys mix it up, biting off their words with chilly precision, is a rare treat.) Stryker, in fulfillment of the disaster foreshadowed in the closing scenes of "X-Men," has essentially declared war on mutants, setting into motion a chain of events that causes some unlikely alliances.

Also new this time around are Stryker's associate Yuriko Oyama (Kelly Hu), aka Deathstrike, who has a specific power that makes her a worthy match for Wolverine (or any adversarial manicurist); Pyro (Aaron Stanford, of "Tadpole"), a simmering cauldron of teen rebellion who, incidentally, can control fire; and a handful of X-kids from Professor Xavier's school, who demonstrate such handy skills as walking through walls and channel-changing by blinking.

And virtually everyone from the original film is back, as is the first film's elegant balance of character-based drama, zippy effects and wry humor. There's also superhero teen romance, as Rogue (Anna Paquin), whose powers make it dangerous for her to touch another, delicately approaches classmate Bobby Drake, aka Iceman (Shawn Ashmore). (Iceman is handy to have around; in a pinch, he can cool a warm Dr. Pepper.) A romantic triangle looms, in the form of Wolverine, Jean Grey (Famke Janssen) and Cyclops (James Marsden). And leading the two X-factions with eagle eyes are Professor Xavier (Stewart), elegant in his silk waistcoats, and the imprisoned, increasingly pale, but ever-intense Magneto (McKellen).

Though "X2" takes time to explore these relationships, it's still an action story, with some sequences staged as breathlessly as a perfectly tuned roller coaster. A nighttime raid on the school, with Wolverine to the rescue like a hairy Superman, may cause a few white knuckles, as will some topnotch X-fights (my favorite: Wolverine and Dreamstrike, hissing like cats).

But Singer's real master stroke is this: These are characters about whom we truly care. There's a welcome, if none-too-subtle, parallel between the mutants and, in real life, anyone who doesn't quite fit in. One scene in "X2," in which a young X-man decides finally to tell his parents about his superpowers, has the ache of a coming-out scene. "Have you tried ... not being a mutant?" asks his mom, while a bitterly angry family member slips away to enact a revenge plot of his own.

And yes, that big X-door is wide open for a sequel at the end of "X2." Thank goodness.